Certain filter assemblies include a filter element located in a housing, where a cover encloses the open end of the housing and provides access to the element for replacement when the element becomes used, worn or spent. The cover has threads on an outer surface thereof which engage cooperating threads on the housing to enable the cover to be easily screwed onto and off of the housing.
One known type of filter element for such a filter housing comprises a sheet of filter material folded to form a plurality of parallel pleats or folds. The side edges of the sheet are brought together so that the sheet has a cylindrical configuration, with the pleats of the sheet extending in the axial or longitudinal direction. The side edges of the sheet are then joined together such as with adhesive, stitching or other means, to retain the filter material in the cylindrical form. The media can be imparted with resin, and/or an outer or inner mesh sheet, weave, mesh or cage can be provided for strength, if necessary or desirable.
Non-pleated media is also known, although pleated media has certain advantages over non-pleated media in some applications, as the pleats provide a large surface area in contact with the fluid to be filtered, which increases the dirt holding capacity and minimizes the pressure loss of the filter element.
The filter media can be coreless, i.e., self-supporting, and received over a cylindrical perforated support tube integral with the filter housing when the element is located in the housing; or can include a cylindrical perforated core integral with the element. End caps are sealingly bonded on either end of the filter element with appropriate adhesive or potting compound being applied between the end caps and the media. One or both of the end caps can have a central opening such that fluid can pass from an inlet, through the media, to an outlet, with particulate and other contaminants being removed by the media. Fluid (air, fuel, oil, hydraulic fluid, etc.) to be filtered typically passes radially inward through the filter media and then outward through the opening in the end cap; however it is also known to have the fluid pass in the opposite manner, that is, through the opening in the end cap, and then radially outward through the media.
One disadvantage with replaceable elements is that when the cover is removed, the element can be saturated with liquid, which can get on the user's hands and clothes as the user attempts to grasp an end cap of the element to remove the element from the housing. Also, it can just be difficult to get one's fingers between the end cap and the housing to grasp the filter element. One solution has been to temporarily connect the element to the cover, such that the user only has to grasp the cover to remove the element from the housing. The element can then be easily removed from the cover when appropriate, and a fresh element attached thereto.
An example of such a solution is shown and described in Popoff, U.S. Pat. No. 6,171,491, which is owned by the assignee of the present invention. In the Popoff design, a pair of lateral projections are provided on an end cap of the filter element, which are received in T-shaped recesses along the inside of the cover. The recesses are formed in an annular sleeve projecting downwardly from the cover, and have both a longitudinally (axially) extending portion and an arcuately (laterally) extending portion. When the cover is screwed off of the housing, the projections enter one of the arcuate portions of the recesses, which thereby retains the element to the cover when the cover is removed. The element can then be easily removed from the cover simply by rotating the element until the projections become aligned with the longitudinal portion, and pulling the element away from the cover (or simply letting the element drop from the cover). An alternative design is also shown in the Popoff patent, where resilient fingers are provided around the end cap, and have tapered, outwardly-extending locking portions which are received in openings spaced around the cover. The fingers retain the element to the cover when the cover is removed from the housing, and the element can be removed from the cover by simply pressing inward on flats of the fingers to disengage the fingers from the cover.
The Popoff designs have received widespread acceptance in the market place as simple techniques for retaining a filter element to a cover when the cover is removed from the housing. Nevertheless, one drawback of such designs is that the cover can be replaced on the housing without an element present. In other words, there is nothing to prevent the user from simply removing the spent element, and then reattaching the cover on the housing without including a fresh element. When the fluid system is thereafter operated, non-filtered fluid can pass through the housing and potentially cause issues with downstream components in the system.
The Popoff designs address this issue by incorporating a valve assembly in a standpipe in the housing, and a projection on the end cap of the element and/or cover to prevent the assembly from being used without an element. The projection must fit within the valve assembly and open a flow path through the filter assembly in order for the filter assembly to be operable. Unfortunately not all filter applications can have such a valve assembly incorporated into the housing. Also, such a valve assembly has a number of parts, which can increase the cost of the assembly.
Alternatively, Oelschlaegel, U.S. Pat. No. 6,146,527, shows a spin-on filter cartridge with a replaceable element which prevents the housing from being attached to a filter head without an element being present. In the Oelschlaegel design, a mounting hub is freely rotatable with respect to a housing, and is rotationally locked with respect thereto, when a series of drive pins on the end cap of the filter element are inserted through openings in the hub and received in corresponding slots in the inside surface of the housing end. While this design prevents the use of the assembly without an element being present, the element is not retained on a cover, and must be directly handled when it is desired to remove the element form the housing.
As such, applicants believe there is a demand in the industry for a filter assembly including a replaceable element and a cover which can temporarily retain the element, whereby the cover and element have cooperating structure to prevent the cover from being attached to the housing without an element present, and which is simple and relatively inexpensive to manufacture.